This project will determine if tamsulosin is useful in patients with a kidney stone. Tamsulosin is used for patients with an enlarged prostate gland, but it has other effects, including relaxing the smooth muscle of the ureters. It is thought that through this mechanism tamsulosin may aid patients with kidney stones that are located in the ureters. This study builds on an earlier placebo controlled double blind trial performed at the George Washington University Hospital that successfully enrolled 109 patients with kidney stones. A further 391 patients will be recruited to that a total of 500 patients will be in the stuy. The sites for the study will be the emergency departments at The George Washington University, the Hospital of University of Pennsylvania and University of Pittsburgh. The primary outcome will be the number of patients who have passed the kidney stone by 30 days after diagnosis. We will also determine if the drug causes other benefits such as reduced pain, less time off work, and a reduced need for surgical intervention.